Axial flow device

ABSTRACT

An axial flow device includes a hub having an outer periphery and a plurality of blades each having a root portion, a tip portion and a body portion between the root portion and the tip portion and projecting outward from the outer periphery of the hub. Furthermore, the root portion has a first angle of attack, the tip portion has a second angle of attack, and the second angle of attack is greater than the first angle of attack. Specifically, each blade is integrally formed based on a continuous angle of attack variation from the root portion through the body portion to the tip portion.

FIELD OF THE INVENTION

The present invention relates to an axial flow device, and in particular, to an axial flow device of which the blades each having a continuous angle of attack variation, in which the angle of attack of the tip portion is greater than the angle of attack of the root portion.

BACKGROUND OF THE INVENTION

Traditionally, blade design of conventional axial flow devices, such as axial flow fans or pumps, can be roughly classified into two kinds as shown in FIG. 1, FIG. 2A and FIG. 2B. In the first kind of blade design as shown in FIG. 1, which is a cross-sectional view of a blade of a conventional axial flow device, the angle of attack of each blade is maintained the same from the root portion to the tip portion, and therefore there is no angle of attack variation between the root portion and the tip portion. In the second kind of blade design as shown in FIG. 2A and FIG. 2B, which are cross-sectional views of the root portion and the tip portion respectively of a blade of another conventional axial flow device, the angle of attack β₂ of the tip portion is less than the angle of attack β₁ of the root portion.

The main purpose of an axial flow device is to overcome resistance while transporting fluid from one point to another, and therefore the key issue is how to provide higher static pressure to overcome resistance so as to increase flow rate. However, both the foregoing blade designs are insufficient to provide higher flow rate while working, and therefore it is usually to increase the revolving speed of the axial flow device or using larger blades for increasing flow rate.

Increasing the revolving speed of an axial flow device relatively increases the flow rate thereof, but it will cause the device to be damaged much faster resulting in a shorter service life. Keeping the blades in balance is another important factor to be taken into account when increasing the revolving speed in order to increase the flow rate. If the blades of the axial flow device are not arranged in balance, the blades will vibrate when starting the axial flow device, affecting the axial flow device quality and its service life. Therefore, it is not a good measure to increase flow rate simply by increasing the revolving speed. Further, increasing the revolving speed also results in waste of power and increase of heat. On the other hand, using larger blades for increasing flow rate is not a good idea as well. Larger blades result in higher manufacturing cost and cause larger size of an axial flow device, which is not practical in industrial applicability. Therefore, there is a need to achieve higher flow rate and improve efficiency of an axial flow device for reducing energy consumption without increasing the fabricating process complexity and manufacturing cost.

SUMMARY OF THE INVENTION

An object of this invention is to provide an axial flow device for providing higher static pressure to overcome resistance so as to achieve higher flow rate and improve efficiency of the axial flow device for reducing energy consumption without increasing the fabricating process complexity and manufacturing cost.

To solve the foregoing problem, the axial flow device of the present invention includes a hub having an outer periphery and a plurality of blades each having a root portion, a tip portion and a body portion between the root portion and the tip portion and projecting outward from the outer periphery of the hub. Furthermore, the root portion has a first angle of attack substantially in a range of 27 degrees to 45 degrees, the tip portion has a second angle of attack substantially in a range of 37 degrees to 55 degrees, and the second angle of attack is greater than the first angle of attack. Specifically, each blade is integrally formed based on a continuous angle of attack variation from the root portion through the body portion to the tip portion, in which the continuous angle of attack variation is substantially in a range of 27 degrees to 55 degrees.

The detailed technology and above preferred embodiments implemented for the present invention are described in the following paragraphs accompanying the appended drawings for people skilled in this field to well appreciate the features of the claimed invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the accompanying advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a cross-sectional view of a blade of a conventional axial flow device.

FIG. 2A is a cross-sectional view of the root portion of a blade of another conventional axial flow device.

FIG. 2B is a cross-sectional view of the tip portion of the blade shown in FIG. 2A.

FIG. 3 is a perspective view of the axial flow device according to one preferred embodiment of the present invention.

FIG. 4 is a top view of the axial flow device shown in FIG. 3.

FIG. 5 is a side view of the axial flow device shown in FIG. 3.

FIG. 6A is a cross-sectional view along line A-A shown in FIG. 4.

FIG. 6B is a cross-sectional view along line B-B shown in FIG. 4.

FIG. 7 is a diagram illustrating the angle of attack variation distribution of each blade of the axial flow device according to one embodiment of the present invention.

FIG. 8A illustrates a blade with a straight planform.

FIG. 8B illustrates a blade which is forwardly skewed.

FIG. 8C illustrates a blade which is backwardly skewed.

FIG. 8D illustrates a blade which is backwardly skewed in the region adjacent to the root portion and forwardly skewed in the region adjacent to the tip portion.

FIG. 8E illustrates a blade which is forwardly skewed in the region adjacent to the root portion and backwardly skewed in the region adjacent to the tip portion.

FIG. 9 illustrates a frame of the axial flow device according to the present invention.

FIG. 10 is a diagram showing the characteristic curves of the axial flow device according to the present invention and the conventional axial flow device shown in FIG. 2A and FIG. 2B.

DETAILED DESCRIPTION OF THE INVENTION

The detailed explanation of the present invention is described as following. The described preferred embodiments are presented for purposes of illustrations and descriptions, and they are not intended to limit the scope of the present invention.

Please refer to FIG. 3, FIG. 4 and FIG. 5. An axial flow device 3 in one preferred embodiment of the present invention, such as an axial flow fan or pump, includes a hub 31 having an outer periphery 311 and a plurality of blades 33, in which each blade has a root portion 331, a tip portion 335 and a body portion 333 between the root portion 331 and the tip portion 335, and projects outward from the outer periphery 311 of the hub 31. Furthermore, the root portion 331 has a first angle of attack α₁ substantially in a range of 27 degrees to 45 degrees as shown in FIG. 6A, the tip portion 335 has a second angle of attack α₂ substantially in a range of 37 degrees to 55 degrees as shown in FIG. 6B, and the second angle of attack α₂ is greater than the first angle of attack α₁. Specifically, as shown in FIG. 5, each blade 33 is integrally formed based on a continuous angle of attack variation from the root portion 331 through the body portion 333 to the tip portion 335, in which the continuous angle of attack variation is substantially in a range of 27 degrees to 55 degrees, and the angle difference α between the second angle of attack α₂ and the first angle of attack α₁, which means α is equal to α₂ minus α₁, is substantially in a range of 6 degrees to 28 degrees.

FIG. 7 is a diagram illustrating the angle of attack variation distribution of each blade 33 of the axial flow device 3 according to one embodiment of the present invention, in which point O illustrates the angle of attack of the root portion 331 and point T illustrates the angle of attack of the tip portion 335. In example 1, which is described by a linear increasing function as shown in FIG. 7, the angle of attack uniformly varies from the root portion 331 through the body portion 333 to the tip portion 335, in which the angle of attack of the tip portion 335 is greater than the angle of attack of the root portion 331 and the angle of attack increases gradually from the root portion 331 to the tip portion 335. In example 2, which is described by an increasing function of which the graph opens up as shown in FIG. 7, the varying rate of the angle of attack increases from the root portion 331 through the body portion 333 to the tip portion 335, in which the angle of attack of the tip portion 335 is greater than the angle of attack of the root portion 331. In example 3, which is described by an increasing function of which the graph opens down as shown in FIG. 7, the varying rate of the angle of attack decreases from the root portion 331 through the body portion 333 to the tip portion 335, in which the angle of attack of the tip portion 335 is greater than the angle of attack of the root portion 331.

FIGS. 8A-8E illustrate several blade designs according to different aspects of the present invention. In FIG. 8A, the blades 33 are “unskewed”: each blade 33 has a straight planform in which a radial center line of the blade 33 is straight and the blade chords perpendicular to the radial center line are uniformly distributed about the line. In FIG. 8B, each blade 33 is forwardly skewed: the blade center line curves in the direction of rotation D of the axial flow device 3. In FIG. 8C, each blade 33 is backwardly skewed: the blade center line curves away from the direction of rotation D of the axial flow device 3. In FIG. 8D, each blade 33 is backwardly skewed in the region adjacent to the root portion 331 and forwardly skewed in the region adjacent to the tip portion 335. In FIG. 8E, each blade 33 is forwardly skewed in the region adjacent to the root portion 331 and backwardly skewed in the region adjacent to the tip portion 335. Moreover, as illustrates in FIG. 9, the axial flow device 3 further includes a frame 4, in which the plurality of blades 33 project outward radially from the outer periphery 311 of the hub 31 toward the frame 4.

The effect of the present invention has been verified in experiments and the results of which are shown in FIG. 10, in which an axial flow device according to the present invention is compared with a conventional axial flow device shown in FIG. 2A and FIG. 2B. As shown in FIG. 10, at the same rotational speed, the axial flow device according to the present invention attains higher static pressure, higher flow rate and overall better performance. Especially, in the characteristic curve of the conventional axial flow device as shown in FIG. 10, there is an instability region, which is the concave section of the curve in the operational area 5, arising from point X1 through point X2, point X3 to point X4, and it causes the conventional axial flow device to surge and stall; however, in the characteristic curves of the axial flow device according to the present invention, the instability region in the operational area 5 is significantly decreased as shown in FIG. 10 and thus it makes the axial flow device more efficient and attains higher flow rate at same static pressure compared with the conventional axial flow device. Accordingly, the axial flow device according to the present invention provides higher static pressure in operational area 5 to overcome resistance so as to achieve higher flow rate and improve efficiency of the axial flow device for reducing energy consumption without increasing the fabricating process complexity and manufacturing cost.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. An axial flow device, comprising: a hub having an outer periphery; and a plurality of blades, wherein each blade has a root portion, a tip portion and a body portion between the root portion and the tip portion and projects outward from the outer periphery of the hub, wherein the root portion has a first angle of attack and the tip portion has a second angle of attack, wherein the second angle of attack is greater than the first angle of attack, wherein the blade is integrally formed based on a continuous angle of attack variation from the root portion through the body portion to the tip portion.
 2. An axial flow device according to claim 1, wherein the continuous angle of attack variation is substantially in a range of 27 degrees to 55 degrees.
 3. An axial flow device according to claim 1, wherein the first angle of attack is substantially in a range of 27 degrees to 45 degrees.
 4. An axial flow device according to claim 1, wherein the second angle of attack is substantially in a range of 37 degrees to 55 degrees.
 5. An axial flow device according to claim 1, wherein the angle of attack uniformly varies from the root portion through the body portion to the tip portion.
 6. An axial flow device according to claim 1, wherein the varying rate of the angle of attack increases from the root portion through the body portion to the tip portion.
 7. An axial flow device according to claim 1, wherein the varying rate of the angle of attack decreases from the root portion through the body portion to the tip portion.
 8. An axial flow device according to claim 1, wherein each blade is forwardly skewed.
 9. An axial flow device according to claim 1, wherein each blade is backwardly skewed.
 10. An axial flow device according to claim 1, wherein each blade is backwardly skewed in the region adjacent to the root portion and forwardly skewed in the region adjacent to the tip portion.
 11. An axial flow device according to claim 1, wherein each blade is forwardly skewed in the region adjacent to the root portion and backwardly skewed in the region adjacent to the tip portion.
 12. An axial flow device according to claim 1, further comprising a frame, wherein the plurality of blades project outward radially from the outer periphery of the hub toward the frame. 